Abstract

This document describes a profile of MathML 3.0 that admits formatting with Cascading Style Sheets.

Status of this Document

This section describes the status of this document at the time
of its publication. Other documents may supersede this document. A
list of current W3C publications and the latest revision of this
technical report can be found in the
W3C technical reports index at
http://www.w3.org/TR/.

A Proposed Recommendation is a specification that is under review by
the W3C Advisory Committee for endorsement as a
W3C Recommendation. It
is is a mature document that has been widely reviewed and has been shown
to be implementable. W3C encourages everybody to implement this
specification. Comments may be sent to the
(archived) public mailing
list www-math@w3.org
(see instructions). When sending e-mail, please
put the text “MathMLCSS-PR” in the subject, preferably like this:
“[MathMLCSS-PR] …summary of comment…”

Publication as a Proposed Recommendation does not imply endorsement by the W3C Membership.
This is a draft document and may be updated, replaced or obsoleted by other
documents at any time. It is inappropriate to cite this document as other
than work in progress.

The previous version of this document was a
Candidate Recomendation.
The only differences between that draft and this are the updated status section.

This Proposed Recommendation specifies a profile of a specification, MathML 3.0
[mathml],
which is itself now being submitted as a Proposed Recommendation, and is intended to accord
with current CSS [css].

During the Candidate Recommendation phase, the Working Group
tested the MathML for CSS Profile using at least two independent CSS implementations.
The Profile contains a suitable CSS stylesheet within the specification itself.
The results of testing,
MathML
for CSS Profile Test Results,
have been made public. The testing used
of parts of the comprehensive MathML
Test Suite.
This is also publicly available.

1 Introduction

The current profile is intended to be subset of MathML 3.0 [mathml] that could be used to capture structure of mathematical formulae
in the way suitable for further CSS formatting. This profile is expected to facilitate adoption of MathML in web browsers and CSS formatters,
allowing them to reuse existing CSS [css] visual formatting model, enhanced with a few mathematics-oriented extensions,
for rendering of the layout schemata of presentational MathML. Development of the CSS profile is assumed
to be coordinated with ongoing work on CSS. As specified in this document a restricted part of MathML3 properly used should
render well with currently implemented CSS up to CSS 2.1. Some descriptions are offered of what might be
done better were a limited set of new properties to be added to CSS3 modules.

It may be useful to note, in connection with the need for this profile, that the CSS2 specification [css2] was developed
and refined at about the same time as the first MathML specification [mathml1]. Now new versions of both MathML and CSS are being created.
This profile is thus part of the ongoing effort to realize the synergy that W3C Recommendations offer to the Web.

1.1 Differences in formatting models

The Math Working Group has identified the following issues, which are considered to be the main obstacles delaying fully consistent MathML/CSS integration.

Insufficient control over vertical alignment of complex inline expressions such as inline tables with multiple rows.

Lack of a mechanism to control stretching of glyphs, or any equivalent functionality, that could be used for sizing of mathematical delimiters and stretchy operators.

Limited scope in the use of selectors and generation of content, which makes it difficult to apply complex formatting to basic structural markup.

The order of children in presentational elements such as mover, munderover, mmultiscripts and mroot does not match their in-flow positions; this makes formatting of such elements more difficult.

Handling of operators, delimiters and accents governed by an operator dictionary (that is by element content rather than attribute values) rather than by explicit markup makes matching of such operators using CSS selectors impossible.

2 Math Elements

2.1 Root element

MathML specifies a single top-level or root math element, which encapsulates each instance of MathML markup within a document.
All other MathML markup must be contained in a math element, which must always be the outermost element of
a MathML expression and can contain an arbitrary number of children. The
math element carries the display attribute that specifies whether
the enclosed MathML expression should be rendered in a display style or an in-line style. Allowed values are "block" and "inline" (default).
It also accepts altimg and alttext attributes that provide fall-back for User Applications (UAs) that do not support MathML layout schemata.
The values of altimg and alttext attributes are URI and CDATA respectively.
All MathML elements should be in the MathML namespace http://www.w3.org/1998/Math/MathML[rec-xmlns].
This can be ensured by adding a default namespace declaration to math elements, or by using namespace prefixes bound to the MathML namespace.

2.2 Token elements and layout schemata

MathML elements included in the current profile can be divided into two classes.
Token elements represent individual symbols, names, numbers, labels, etc. In general, tokens can have only character data as content.
Layout schemata build expressions out of parts, and can only have elements as content except for whitespace, which they ignore.
There are also a few empty elements used only in conjunction with specific layout schemata.

All individual "symbols" in a mathematical expression should be
represented by MathML token elements. The primary MathML token element
types are identifiers (e.g. variables or function names), numbers, and
operators (including fences, such as parentheses, and separators, such
as commas). There are also token elements for representing text or
whitespace that has more aesthetic than mathematical significance,
and for representing "string literals" for compatibility with
computer algebra systems. Note that although a token element
represents a single meaningful "symbol" (name, number, label,
mathematical symbol, etc.), such symbols may be comprised of more than
one character. For example sin and 24 are
represented by the single tokens <mi>sin</mi>
and <mn>24</mn> respectively.

Token elements included in the current profile are summarized in the table below.

mi

identifier

mn

number

mo

operator, fence or separator

mtext

text

mspace

space

ms

string literal

In traditional mathematical notation, expressions are recursively
constructed out of smaller expressions, and ultimately out of single
symbols, with the parts grouped and positioned using one of a small
set of notational structures, which can be thought of as "expression
constructors". In MathML, expressions are constructed in the same way,
with the layout schemata playing the role of the expression
constructors. The layout schemata specify the way in which
sub-expressions are built into larger expressions. The terminology
derives from the fact that each layout schema corresponds to a
different way of "laying out" its sub-expressions to form a larger
expression in traditional mathematical typesetting.

Basic expression constructions included in the current profile are listed in the table below.

mrow

groups any number of sub-expressions horizontally

mfrac

forms a fraction from two sub-expressions

msqrt

forms a square root (radical without an index)

mroot

forms a radical with specified index

merror

encloses a syntax error message from a preprocessor

mphantom

makes content invisible but preserve its size

mfenced

surrounds content with a pair of fences

menclose

encloses content with a stretching symbol

msub

attaches a subscript to a base

msup

attaches a superscript to a base

msubsup

attaches a subscript-superscript pair to a base

munder

attaches an underscript to a base

mover

attaches an overscript to a base

munderover

attaches an underscript-overscript pair to a base

mmultiscripts

attaches prescripts to a base

mtable

marks a table or matrix

mtr

marks a row in a table or matrix

mtd

marks a one entry in a table or matrix

mstack

used for elementary math notations such as 2D addition, subtraction and multiplication

mlongdiv

used for elementary math notations for long division

msline

marks horizontal line in elementary math layouts

msrow

marks row in elementary math layouts

maction

binds actions to a sub-expression

2.3 Required Arguments

Some layout schemata require a specific number of arguments, for example mfrac is supposed to have two child elements
representing numerator and denominator. In the current profile, layout schemata with fixed number of required arguments
accept only elements mrow, maction, merror, mphantom and tokens
mi, mn, mo, ms, mtext as child elements.
This restrictions is imposed to ensure that each part of layout schemata has its own containing block and is uniquely represented in the
document object model. For example nested fractions where the numerator or denominator
are themselves fractions

The number of arguments required by a particular layout schemata element is specified in the table below.
Note that in the current profile, the content model of mfenced and maction is stricter
compared to what is allowed by MathML 3.0 specification.

Element

Required argument count

Argument roles

mfrac

2

numeratordenominator

mroot

2

baseindex

mfenced

1

base

msub

2

basesubscript

msup

2

basesuperscript

msubsup

3

basesubscriptsuperscript

munder

2

baseunderscript

mover

2

baseoverscript

munderover

3

baseunderscriptoverscript

mmultiscripts

4

basemprescriptspresubscriptpresuperscript

mtable

1+

one or more mtr elements

mtr

1+

one or more mtd elements

mstack

4+

one or more mn tokens followed by msrow element, msline and
groups consisting of one or more mn tokens followed by optional msline

mlongdiv

3+

result of the division followed by divisor and
groups consisting of one or more mn tokens followed by optional msline

msrow

2

mo token element followed by mn token

maction

2

basetooltip

The elements mrow, msqrt,
merror, mphantom,
menclose, mtd
and math admit any number of arguments and accept any layout schemata or token elements from current profile as children.

2.4 Common attributes

The attributes id, class and style can be used on any element included in the current profile:
id provides a mechanism for annotating elements with unique identifiers,
class assigns one or more class names to an element and
style specifies style information for the current element.
The attribute mathvariant is allowed on nonempty token elements,
attribute is included in the profile for interoperability reasons to ensure
that font changes are transparent for CSS unaware UAs.

The following table lists common attributes, their values and the elements on which they can be used.

3 Token Elements

Token elements in presentation markup are, broadly speaking, intended to
represent the smallest units of mathematical notation which carry
meaning. Tokens are roughly analogous to words in text. However,
because of the precise, symbolic nature of mathematical notation, the
various categories and properties of token elements figure prominently in
MathML markup. By contrast, in textual data, individual words rarely
need to be marked up or styled specially.

Frequently tokens consist of a single character denoting a
mathematical symbol. Other cases, e.g., function names, involve
multi-character tokens. Further, because traditional mathematical
notation makes extensive use of symbols distinguished by their
typographical properties, care must be taken to ensure that styling
mechanisms respect typographical properties which carry meaning.
Consequently, characters, tokens, and typographical properties of
symbols are closely related to one another in MathML.

3.1 Identifier <mi>

An mi element represents a mathematical identifier; its rendering
consists of the text content displayed in a typeface
corresponding to the mathvariant attribute.
Since the typeface used can distinguish similar identifiers,
it often serves an important semantic function.

In MathML 3.0, the default value of mathvariant depends
on the content of the element, it is
"italic" for single character content (e.g.,
<mi>x</mi>) and
"normal" otherwise (e.g., <mi>sin</mi>).
Such behavior does not fit well in the scope of CSS,
therefore in current profile "italic" is the default value
regardless of the element content
and mathematical identifiers for which a non-italic typeface is desired
(e.g., multi-character identifiers), must explicitly specify
the mathvariant attribute.

3.2 Number <mn>

An mn element represents a "numeric literal" or other data that should be rendered as a numeric
literal. Generally speaking, a numeric literal is a sequence of digits, perhaps including a decimal point, representing
an unsigned integer or real number.

A typical graphical renderer would render an mn element as the characters of its content, with
no extra spacing around them (except spacing from neighboring elements such as mo).

3.3 Operator <mo>

An mo element represents an operator or anything that should be rendered as an operator.
In MathML the list of things that should "render as an operator" is widely inclusive.
Besides ordinary operators with infix, prefix, or postfix forms, fence characters such as braces, parentheses,
and separators such as comma and semicolon are included.
In the current profile the mo element is not expected to produce vertically stretchable delimiters; instead the mfenced element
should be used for vertically stretchy delimiters
such as stretchy brackets, braces, parentheses and vertical bars.

Note also that this profile does not rely on an operator dictionary, but instead it is recommended to mark fences,
separators and large operators explicitly using fence, separator and largeop attributes.
In addition, prefix, infix and postfix operators may be distinguished using the form attribute.
In the present profile, the default value of this attribute is "prefix" if
the mo element is the first child of a parent element that has many children,
and "postfix" if mo element is the last child of a parent with multiple children;
the value is "infix" in all other cases.
Those mo tokens that represent fences such as brackets, braces, parens and vertical bars should be marked using the fence attribute,
separators such as comma and semicolon should be marked using the separator attribute, while
large operators such as sums, products and integrals may be labeled using the largeop attribute.
UAs may rely on these attribute to infer default spacing around operators.

In the present profile stretchy operators are defined by the stretchar attribute's specifying a stretchy character to replaces the content of an mo element.
The specified character is supposed to stretch to fill the available space (height of line box in case of vertically stretchy delimiters and the
available width in case of horizontally stretchy delimiters). UAs that do not recognize
a character specified by an stretchar attribute as stretchy
should ignore the attribute and display the content of the mo element instead.

Name

values

default

form

prefix | infix | postfix

depends on position of mo element, see exact rules above

fence

true | false

false

separator

true | false

false

largeop

true | false

false

stretchar

character

none

3.4 Text <mtext>

An mtext element is intended to denote commentary text.

3.5 Space <mspace>

An mspace empty element represents a blank space of any desired size, as set by its attributes. It can also be
used to make linebreaking suggestions to a visual renderer.

The width attribute defines the width of the space produced by an mspace element. The default value is zero.
Named values are described in table below.

Named space

value (em)

verythinmathspace

1/9

thinmathspace

1/6

mediummathspace

2/9

thickmathspace

5/12

verythickmathspace

1/3

The linebreak attribute is used to give a linebreaking hint to a visual renderer.
Attribute values are defined in table below.

Value

Description

auto

default linebreaking algorithm (implementation dependent)

newline

start a new line

goodbreak

if a linebreak is needed on the line, here is a good spot

In the case when both the width attribute and the linebreak attribute are set, the linebreak attribute is ignored.

3.6 String Literal <ms>

The ms element is used to represent "string literals" in expressions meant to be interpreted by
computer algebra systems or other systems containing "programming languages". By default, string literals are displayed surrounded by
double quotes.

In visual renderers, the content of an ms
element is typically rendered with no extra spacing added around the
string, and quote characters at the beginning and the end of the
string. By default, the left and right quote characters are both the
standard double quote character ". However, these characters can be changed with the lquote and
rquote attributes defined below.

Name

values

default

lquote

string

"

rquote

string

"

4 General Layout Schemata

Besides tokens there are several families of MathML presentation
elements. One family of elements deals with various
"scripting" notations, such as subscript and
superscript. Another family is concerned with matrices and tables. The
remainder of the elements, discussed in this section, describe other basic
notations such as fractions and radicals, or deal with general functions
such as action binding and error handling.

4.1 Horizontally Group Sub-Expressions <mrow>

An mrow element is used to group together any
number of sub-expressions, usually consisting of one or more mo elements acting as "operators" on one
or more other expressions that are their "operands".

4.2 Fractions <mfrac>

The mfrac element is used for fractions. It can also
be used to mark up the presentation of fraction-like objects such as binomial
coefficients and Legendre symbols. The syntax for mfrac
is:

<mfrac> numerator denominator </mfrac>

In addition to common attributes, mfrac has additional
attributes that could be used to control horizontal alignment of
numerator and denominator and thickness of fraction bar.

Name

values

default

linethickness

0 | 1 | 2 | medium | thick

1

numalign

left | center | right

center

denomalign

left | center | right

center

The linethickness attribute indicates the thickness
of the horizontal "fraction bar", or
"rule", typically used to render fractions. Value "0"
indicates that no bar should be rendered, value "1" (the same as "medium") refers to default width
of fraction bar and "2" ("thick") produces bold fraction bar.

The numalign and denomalign attributes
control the horizontal alignment of the numerator and denominator,
respectively. Typically, numerators and denominators are
centered.

4.3 Radicals <msqrt>, <mroot>

These elements construct radicals. The msqrt element is
used for square roots, while the mroot element is used
to draw radicals with indices, e.g., a cube root. The syntax for these
elements is:

<msqrt> base </msqrt>
<mroot> base index </mroot>

The mroot element requires exactly 2 arguments. However, msqrt accepts any number of arguments.

4.4 Error Message <merror>

The merror element displays its contents as an "error message". The contents can be any expression or expression sequence.

4.5 Making Sub-Expressions Invisible <mphantom>

The mphantom element renders its content as invisible, but
with the same size and other dimensions, including baseline position,
that its contents would have if they were rendered
normally; mphantom can be used to align parts of
an expression by invisibly duplicating sub-expressions.

4.6 Expression Inside Pair of Fences <mfenced>

The mfenced element provides a convenient way of expressing common constructs involving fences (i.e., braces, brackets, and parentheses).
The size of the fences depends on the size of the expression enclosed by the fence element. Opening and closing fences are specified using the open
and close attributes defined below. This profile does not allow an mfenced element to have multiple children;
authors are encouraged to group multiple children into one mrow element if this can be done.

Name

values

default

open

CDATA

(

close

CDATA

)

4.7 Enclose Expression Inside Notation <menclose>

The menclose element renders its content inside the enclosing notation specified by its notation attribute, menclose accepts any number of arguments.

The values allowed for notation are open-ended. Conforming renderers may ignore any value they do not handle, although
renderers are supposed to recognize at least the values listed below.

Name

values

notation

box | left | right | top | bottom | horizontalstrike

The value "box" can be used to enclose content of the element in a frame.
The values "left", "right", "top" and
"bottom" should result in lines drawn on the corresponding sides of
the contents, "horizontalstrike" should result in strikeout lines being superimposed over the content of the
menclose.

5 Script and Limit Schemata

The elements described in this section position one or more scripts
around a base. In addition to subscript and superscript elements,
MathML has overscript
and underscript elements that place scripts above and below the base.

Because presentation elements should be used to describe the abstract
notational structure of expressions, it is important that the base
expression in all "scripting" elements (i.e., the first
argument expression) should be the entire expression that is being
scripted, not just, as has been common, the rightmost character.

5.1 Subscript <msub>

The syntax for the msub element is:

<msub> base subscript </msub>

The element is used to attach a subscript to a base.

5.2 Superscript <msup>

The syntax for the msup element is:

<msup> base superscript </msup>

The element is used to attach a superscript to a base.

5.3 Subscript-superscript Pair <msubsup>

The msubsup element is used to attach both a subscript and a superscript to a base expression.

The syntax for the msubsup element is:

<msubsup> base subscript superscript </msubsup>

5.4 Underscript <munder>

The syntax for the munder element is:

<munder> base underscript </munder>

The element is used to attach an underscript below a base.

5.5 Overscript <mover>

The syntax for the mover element is:

<mover> base overscript </mover>

The element is used to attach an overscript over a base.

5.6 Underscript-overscript Pair <munderover>

The syntax for the munderover element is:

<munderover> base underscript overscript</munderover>

The element is used to attach both an underscript and an overscript to a base.

5.7 Prescripts <mmultiscripts>

This element allows adding pairs of prescripts to one base expression. Missing scripts can be represented by the empty element none.

The argument sequence consists of the base followed by an empty element mprescripts
and a pair of, vertically aligned, a presubscript and a presuperscript.

6 Tables and Matrices

Matrices, arrays and other table-like mathematical notation are marked
up using mtable,
mtr, and mtd elements. These elements are similar to the
table, tr and td elements of XHTML.

6.1 Table or Matrix <mtable>

A matrix or table is specified using the mtable element.

The following attributes may be used to specify alignment and to add frames and rules to the table.

Name

values

default

rowalign

top | bottom | center | baseline

baseline

columnalign

left | center | right

center

rowlines

none | solid | dashed

none

columnlines

none | solid | dashed

none

frame

none | solid | dashed

none

Note that the default value for each of rowlines, columnlines and
frame is the literal string
none, meaning that the default is to render no lines,
rather than that there is no default.

The rowalign attribute specifies how the entries in
each row should be aligned. For example, "top" means that the tops of
each entry in each row should be aligned with the tops of the other
entries in that row. The columnalign attribute specifies
how the entries in each column should be aligned.

6.2 Row in a Table or Matrix <mtr>

An mtr element represents one row in a table
or matrix. An mtr element is only allowed as a
direct sub-expression of an mtable element, and
specifies that its contents should form one row of the table. Each
argument of mtr is placed in a different column
of the table, starting at the leftmost column.

The following attributes may be used to specify alignment

Name

values

default

rowalign

top | bottom | center | baseline

inherited

columnalign

left | center | right

inherited

The rowalign and columnalign attributes allow a specific row to
override the alignment specified by the same attributes in the
surrounding mtable element.

6.3 Entry in a Table or Matrix <mtd>

An mtd element represents one entry, or cell, in a
table or matrix. An mtd element is only
allowed as a direct sub-expression of an mtr.

The following attributes may be used to specify alignment

Name

values

default

rowalign

top | bottom | center | baseline

inherited

columnalign

left | center | right

inherited

The rowalign and columnalign attributes
allow a specific matrix element to override the alignment specified by
a surrounding mtable or mtr
element.

7 Elementary Math

7.1 2D addition, subtraction and multiplication <mstack>

Table like structures in elementary math notations such as 2D addition, subtraction and multiplication
can be produced using mstack layout schemata. Vertical alignment of mstack
is specified by align attribute. In current profile horizontal alignment of numbers within mstack
simply defaults to right,
as current CSS implementations are unlikely to handle more sophisticated alignment mechanisms for mstack
layout schemata.

Name

values

default

align

top | bottom | center | baseline

baseline

stackalign

right

attribute is required

Element contains one or more mn
tokens followed by msrow element, msline and groups consisting of one or more
mn tokens followed by optional msline.

The syntax for the mstack element is:

<mstack stackalign="right">
(one or more mn tokens)
(msrow element)
<msline/>
(one or more mn tokens followed by optional msline)+
</mstack>

7.2 Horizontal rows <mrow>

In the present profile msrow element is used to add operator before
last operand in elementary math notations such as 2D addition, subtraction and multiplication.

Element contains mo token followed by
mn token

The syntax for the msrow element is:

<msrow><mo>operator</mo><mn>operand</mn></msrow>

7.3 Long division <mlongdiv>

Elementary math notations for long division can be produced using mlongdiv layout schemata.
Vertical alignment of mlongdiv is specified by align attribute.
In current profile horizontal alignment of numbers within mlongdiv simply defaults to left,
as current CSS implementations are unlikely to handle more sophisticated alignment mechanisms for mlongdiv
layout schemata.

Name

values

default

align

top | bottom | center | baseline

baseline

stackalign

left

attribute is required

Element contains mn token representing result of the division followed by
mn token representing divisor and
groups consisting of one or more mn tokens followed by optional msline element.

The syntax for the mlongdiv element is:

<mlongdiv stackalign="left">
(result of the division)
(divisor)
(one or more mn tokens followed by optional msline)+
</mlongdiv>

8 Annotations

8.1 Bind Action to a Sub-Expression <maction>

To provide a mechanism for binding actions to expressions, MathML provides the maction element.
The action type is specified by the actiontype attribute. Current profile defines only "tooltip" actiontype.

Name

values

default

actiontype

tooltip

(required attribute, no default value)

<maction actiontype="tooltip"> base tooltip </maction>

When a mouse cursor is placed over an expression UAs that support this action type should display the content of the second child in a "tooltip" box.

8.2 Add semantic mapping <semantics>

The current profile deals with layout schemata that reflect the visual structure of mathematical formulae.
To attach extra semantic information that describes the content of formulae or provide an alternative encoding
of a mathematical expression one can use the Content MathML semantics element.
In current profile content model of semantics element is limited to presentational MathML
followed by annotation and/or annotation-xml elements.

9 Extensibility and Conformance

9.1 Extensibility

Since the current profile is designed to be suitable for use in an XML/CSS environment, it is relatively easy to extend it by adding new elements or attributes
[rec-xml] to a DTD and specifying the default formatting in a style sheet.
However any new elements should be placed in their own namespace and any new attributes added to existing MathML elements should have a namespace prefix;
authors and implementers are strongly encouraged to use standard markup whenever possible.
Similarly, maintainers of documents employing MathML extension mechanisms are encouraged to monitor relevant standards activity
and to update documents to use more standardized markup as it becomes available.

9.2 Conformance

Documents that conform to this MathML for CSS profile should be conformant MathML 3.0 documents and should use only those MathML elements and attributes included
in the current profile. The content of layout schemata with a fixed number of arguments should match the content model specified in the
list of required arguments and the profile's DTD.

UAs that conform to the MathML for CSS profile should support all MathML elements and attributes included in profile.
When a conformant UA encounters an element that it does not recognize it may ignore that element, but should process its content.
UAs that support the standard DOM are encouraged to expose such elements through generic DOM Element interface. UAs that support style sheets
are encouraged to apply formatting specified in style sheets to such elements.

The changes affect the handling of an mi token element. In this MathML for CSS profile,
the default value of the mathvariant attribute is "italic",
regardless of the content of the element.
For interoperability reasons, authors should specify the value of this attribute explicitly if an mi
token contains more then one character.

The MathML for CSS profile does not rely on an operator dictionary because CSS selectors can not differentiate between mo
tokens based on their content.
Therefore authors are encouraged to use more explicit markup when applicable: for example, stretchy vertical delimiters are better marked
using the mfenced construction, and stretchy over or under bars and strikes are better marked using the menclose element.
In addition, there are form, fence, separator, largeop, stretchar attributes that
can be used to specify the class of an operator.

In the MathML for CSS profile the mfenced schema is simplified. In particular, the separators attribute of an mfenced element is dropped,
as there is no way to handle the separator attribute in the present CSS framework. For interoperability reasons,
since the attribute does not have an empty default value, the content model was restricted to allow only one child element.

Multiscripts schemata is included in the profile but number of scripts is limited to at most two prescripts. It is difficult to handle mmultiscripts construction as the order of child elements inside a mmultiscripts element does not match their in-flow order.

The table model is simplified: the mlabeledtr element is dropped as it does not fit in the CSS table model,
and many attributes have been removed.

Layout schemata with fixed number of required arguments accept only elements mrow, maction, merror, mphantom and tokens
mi, mn, mo, ms, mtext as child elements.
This restrictions is imposed to ensure that each part of layout schemata has its own containing block and is uniquely represented in
document object model.

12 Default CSS style sheet

(this section is non normative)

This profile admits a default CSS style sheet that could be used to render MathML in CSS aware UAs.
In the long term perspective it would be appropriate to extend CSS3 with a few math specific properties,
until then one can use style sheet enclosed below for formatting of MathML defined in the current profile.